Power supplies in, for example, telephone communication systems, are typically designed to power only thirty to forty percent of the station sets and lines connecting thereto. This design criterion is based on probability studies that show that during a typical busy hour, only thirty to forty percent of the lines connecting to a group of port circuits that share a power supply are busy at any one time. However, a problem arises with these power schemes when traffic is not equally graded across such groups. For example, in typical user-maintained business communication systems it is likely that unbalanced traffic grading will occur across the switch as a result of system growth.
In an architecture where, for economic and reliability reasons, separate modular power supplies are provided for each shelf, or circuit carrier, of plug-in circuit cards, one or more circuit carrier power supplies will most likely experience an overload due to improper traffic grading, thereby resulting in degraded service or a circuit carrier power failure. An obvious solution to this problem is to provide larger circuit carrier power supplies to account for improper or unbalanced traffic across circuit carriers. This approach, however, is unduly expensive.
Further, prior power distribution arrangements typically include a large centralized power supply for supplying system power. Such arrangements can include a large battery that is used to supply system power whenever the centralized power arrangement becomes inoperable. Typically, the reserve battery continues to supply power until its capacity diminishes to a point where it cannot properly power the system. Thereafter, when the centralized power system is restored to service, the battery is recharged. Typically, the time required to fully recharge a discharged battery is very long. Thus, communication systems using such power arrangements are usually disabled for quite a period of time if the centralized power system becomes inoperable during the battery recharge period.